reciprocating compressor
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RECIPROCATING COMPRESSORS
RECIPROCATING COMPRESSORS
CompressorsCompressors
HIGH LOWV. HIGH
NO NOYES
YESNO YES
LOW HIGH V. HIGH
YES NO NO
Pressure PPressure P
Flow Rate QFlow Rate Q
S .R .VS .R .V
EfficiencyEfficiency
Maint. costMaint. cost
PulsationPulsation
SurgingSurging
Reciprocating Centrifugal Axial
V. HIGH LOW LOW
LOW HIGH V. HIGH
Crosshead
Stuffing
Box
Packing
Discharge Valves
Suction Valves
PistonDistance Piece
Con-rodCrank
Piston Rod
Wiper
Rings
POWER END POWER END
GASEND
GASEND
FIXED CLEARANCE
VOLUME
VARIABLECLEARANCE
VOLUME
RECIPROCATING COMPRESSORS:FLOW RATE REGULATION
RECIPROCATING COMPRESSORS:FLOW RATE REGULATION
• VARIABLE CLEARANCE
• VARIABLE SPEED
• BYPASS
• SUCTION VALVE
UNLOADERS
CF CR
CF = C
CR = C
23
13
• VARIABLE CLEARANCE• VARIABLE CLEARANCE
C = Total Clearance Volume = CF + CR
Before operating Before operating
After operating After operating
CF CR
CF = C
CR = C
12
12
Point g suction valves open
C = Clearance volume
C
v
b
a
c
g
Pd
Ps c1M
EFFECT OF CLEARANCE VOLUME
EFFECT OF CLEARANCE VOLUMEAtAt
Point a suction valves closed
Point b discharge valves open
Point c discharge valves closed
Compression ratio
Pressure ratio )ABSOLUTE(P d
P s=
Volumetric efficiency =V a g
V cylinder a M
a g=
= V cylinder
V b M
C
vb a
c
g
Pd
Ps c1M
b
b M
a M =
C
v
Pd
Ps c1M
b
a
c
g
Volumetric efficiency =V a g
V cylinder a M
a g=
C
v
Pd
PsM
b
a
c
g
Volumetric efficiency =V a g
V cylinder a M
a g=
v
Pd
Ps M
C
g a
bc
Volumetric efficiency =V a g
V cylinder a M
a g=
If C Increased suction valves will open at ( g (
C
va
c
g
Pd
Ps
b
M
EV DECREASES
Q DECREASES
Volumetric efficiency =V a g
V cylinder a M
a g=
If C Decreased suction valves will open at ( d (
C
va
c bPd
Ps M g
EV INCREASES
Q INCREASES
Volumetric efficiency =V a g
V cylinder a M
a g=
•SUCTION VALVE
UNLOADERS
•SUCTION VALVE
UNLOADERS
STUFFING BOX
RIDER RINGSRIDER RINGS
PRESSURE RINGS
PRESSURE RINGS
WIPER RINGS
WIPER RINGS
T
R
TANGENTIAL RINGST
R RADIAL RINGS
RECIPROCATING COMPRESSORS
INTERMEDIATEPRESSURES
RECIPROCATING COMPRESSORS
INTERMEDIATEPRESSURES
Example 1
4 Stages Reciprocating Air comp has outlet pressure P4 = 80 barg
what are the intermediate pressures
P0
0 barg
1st
stage
P1
2nd stage
P2
3rd stage
P3 P4
80 barg
4th stage
P0
0 barg
P1 P2 P3 P4
80 barg
1st
stage2nd
stage3rd
stage
4th stage
R =P1
P0
P4
P3=
P3
P2=
P2
P1=
Assume
R is The equal Pressure Ratio between stages.
R = 4 P4
P0RT =
P4
P0BUT
RTR =
4
AND RT = P4
P0
R = RT4
Generally
R = RTN
P4 = R * P3 = 3 * 27 = 81 bara = 80 barg
P0
0 barg
P1 P2 P3 P4
80 barg
1st
stage2nd
stage3rd
stage
4th stage
RT = P4 / P0 = (80 +1) / (0 +1) = 81/ 1 = 81
N 4R = RT = 81 = 3
P1 = R * P0 = 3 * 1 = 3 bara = 2 barg
P2 = R * P1 = 3 * 3 = 9 bara = 8 barg
P3 = R * P2 = 3 * 9 = 27 bara = 26 barg
Example 2
3 Stages Reciprocating Gas compressor has Outlet pressure P3 = 127 barg Inlet pressure P0 = 1 barg
what are the intermediate pressures
P0
1 barg
1st
stage
P1
2nd stage
P2
3rd stage
P3
127 barg
P0
1 barg
1st
stage
P1
2nd stage
P2
3rd stage
P3
127 barg
Assume
P3
P2=P1
P2=R
P1
P0
=
RTP3
P0
=3
RP3
P0
=BUT
3R
P3
P0
=
R = RT3 3
R = RT
P3 = R * P2 = 4 * 32 = 128 bara = 127 bar g
3R = RT = 64 = 4
=)127+ 1(
)1+1(=
1282 = 64
P1 = R * P0 = 4 * 2 = 8 bara = 7 bar g
P2 = R * P1 = 4 * 8 = 32 bara = 31 bar g
P3
P0
3R=RT =
Example 2
3 Stages Gas compressor has Outlet pressure = 255 bar gInlet pressure = 3 bar g
What are the intermediate pressures
P0
3 barg
1st
stage
P1
2nd stage
P2
3rd stage
P3
255 barg
P0
3 barg
1st
stageP1
2nd stage
P2
3rd stage
P3
255 barg
P3 = R * P2 = 4 * 64 = 256 bara = 255 bar g
3R = RT = 64 = 4
=)255+ 1(
)3+1(=
2564 = 64
P1 = R * P0 = 4 * 4 = 16 bara = 15 bar g
P2 = R * P1 = 4 * 16 = 64 bara = 63 bar g
P3
P0
3R=RT =
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